BioEd Online

Eye cells transplanted into the brain have mitigated the symptoms of Parkinson's disease in a preliminary trial involving six patients. The findings of the small study suggest that injections of such cells can partly reverse the motion difficulties associated with the illness.

The eye cells seem to produce a natural form of a drug that is frequently given to patients, but release it in a steady, even flow that prevents some of the nasty side-effects of the medicine.

Parkinson's disease is a debilitating neurological disorder thought to affect brain cells' ability to produce the powerful cell-signalling molecule dopamine. For the past three decades, patients with this disorder have typically received a medication called levodopa (L-DOPA), which replaces lost dopamine.

Doses of L-DOPA help to alleviate some of the symptoms of Parkinson's disease, which include tremor, muscle rigidity and slowed motion. But only for a while.

Over time, patients respond less and less to L-DOPA. But upping the dosage can lead to a side-effect known as dyskinesias: involuntary movements resulting in fragmented or jerky motions.

Some scientists believe that taking L-DOPA pills injects too much of the drug into the body in a single dose, over-exciting and damaging certain cells. So researchers have sought a way to provide the brain with a relatively low and constant supply of the compound.

Brain boost

Experts knew that certain cells in the back of the eye produce natural L-DOPA, so they reasoned that these cells could provide a stable supply of the compound if transferred to a patient's body. Experiments in animals supported this idea.

Natividad Stover of the University of Alabama in Birmingham and her colleagues recruited six patients with advanced Parkinson's disease for their preliminary study. Each volunteer received an injection of about 325,000 of the L-DOPA-producing cells, known as human retinal pigment epithelial cells, taken from post-mortem eye tissue.

The researchers have tracked the patients for two years so far, and have found no signs of transplant rejection. Two years after the operation, patients reported that they felt their treatment was working 65% of the time, up from 44% prior to the transplant. A similar improvement was seen in physical tests of motor control, and incidence of dyskinesias also dropped. The findings from this preliminary trial appear in the journal Archives of Neurology¹.

Stover and her co-authors say that the next step will be to conduct a randomized, placebo-controlled study in which patients remain unaware of the type of treatment they receive.